The copending application of Burack et al., Ser. No. 07/936,484, filed Aug. 28, 1992, hereby incorporated herein by reference, describes a method for making optical backplanes by using a robotic routing machine to apply optical fibers to a flat surface of a flexible plastic substrate. The fibers are bonded to the substrate surface by a pressure-sensitive adhesive, and after routing they are covered by a plastic sheet that encapsulates them to protect them, to give the structure mechanical stability, and to keep the optical fibers in place during the handling of the optical backplane. The optical fibers of the optical backplane are typically used as large-capacity transmission lines between printed wiring boards or between optical circuits.
The patent application describes how a computer is used to provide optical fibers of the appropriate length between input and output ports, or tabs, of the optical backplane, it being important for optical transmission reliability that there not be minute deviations in the prescribed length of the line. The optical fibers are of course made of glass and are therefore susceptible to damage, particularly at locations at which the fibers overlap or cross over one another. In appluing a plastic encapsulation to the optical fibers after routing, it has been found that some of the optical fibers tend to break and other optical fibers tend to become displaced from their assigned physical positions. Further, it is difficult to bond reliably the optical fibers within a plastic composite structure such that the fibers are firmly mechanically supported in place even while free ends of the fibers are manipulated to interconnect the optical backplane to other structures. Finally, it would be desirable to be able to peel back the encapsulation to expose ends of optical fibers so that they could be interconnected with other apparatus.
Accordingly, there is a continuing need for techniques for encapsulating optical fibers on a flexible plastic substrate that are consistent with the requirements of mass production, which do not require great operator skill, which provide long-life structural support and protection to optical fibers, which maintain predetermined fiber placement, and which can be manipulated to expose optical fiber ends if necessary.